Tag: introduction to reproduction

Sponges and Cnidarians are among the animals, that can reproduce by budding. A small part of the parent's body separates from the rest and develops into a new individual. Sometimes the buds remain attached and become more or less independent members of a colony. In some tunicate colonies, different individuals are connected by root-like structures called stolons. In others, they share body parts, such as their atrial (exhaling) siphon. These tunicates reproduce asexually through budding example Botryllus schlosseri. The scyphistoma reproduces asexually, producing similar polyps by budding, and then either transforming into a medusa or budding several medusae off from its upper surface. The medusae are initially microscopic and may take years to reach sexual maturity. So, the correct answer is option D.

Parthenogenesis (virgin development) is a form of asexual reproduction in which an unfertilized egg develops into an adult animal. The adult is typically haploid. Parthenogenesis is common among insects (especially honeybees and wasps, aphids etc.) and crustaceans; it also occurs among some other invertebrate and vertebrate groups, including some species of nematodes, gastropods, fishes, amphibians, and reptiles. Although a few species appear to reproduce solely by parthenogenesis, in most species episodes of parthenogenesis alternate with periods of sexual reproduction. Parthenogenesis may occur for several generations, followed at some point by sexual reproduction in which males develop, produce sperm and mate with the females to fertilize their eggs. In some species, parthenogenesis is a means of rapidly producing individuals when conditions are favorable.

Parthenogenesis refers to the development of an individual from unfertilized eggs. In honey bees, parthenogenesis is common and here, drones develop as a result of parthenogenesis only. The mode of parthenogenesis is arrhenotoky in which only females are produced. Frog and sea urchin reproduces by artificial parthenogenesis.

Maturation of the follicle is stimulated by follicle stimulating hormone (FSH) from the anterior pituitary, and oestrogen secreted by the follicle lining cells. Ovulation is triggered by a surge of luteinising hormone (LH) from the anterior pituitary, which occurs a few hours before ovulation. After ovulation, the follicle lining cells develop into the corpus luteum (yellow body), under the influence of LH from the anterior pituitary. The corpus luteum produces the hormone progesterone and some oestrogen. If the ovum is fertilised it embeds itself in the wall of the uterus where it grows and develops and produces the hormone human chorionic gonadotrophin (hCG), which stimulates the corpus luteum to continue secreting progesterone and oestrogen for the first 3 months of the pregnancy and, after which time this function is continued by the placenta.

Frogs reproduce by external fertilisation. The female frog ovulates in the water and releases its gametes. The sperm released from the male frog fertilizes to form zygote which turns into a well-developed egg. So, the correct answer is option B.

• Secondary sexual characters are those that appear at the time of puberty while the primary sexual characters are present from the time of birth. 
• These secondary sexual characters are caused by hormones released at the time of puberty.
• Beard growth starts in the male at the time of puberty in the male because of increased secretion of testosterone.

Fertilization can be internal or external. When the fertilization occurs inside the female body, then it is internal fertilization (e.g., most reptiles, some birds, some fishes.)
Fertilization in dogfish, shark is internal. While in catfish, toads and some frogs, it is external fertilization.
Hence, the correct answer is option (C).

Testes are the organs that produce the germ cells and scrotum is the pouch that contains the testes. The evolution of the scrotal sacs in mammals has been mysterious and there exist many hypotheses to explain the probable function of the scrotum. Primarily they provide a space, that isolate and serves to provide a temperature, lower than the body; essential for the production, maturation, and storage of sperm cells. Bats in this respect are unique and exhibit testicular migration between abdomen and scrotum, while the cauda epididymis is permanently in the scrotal sacs.

Bidder's canal is present in male frogs. Vasa-efferentia opens into the Bidder's canal and the Bidder's canal is connected to longitudinal collecting tubules by means of a number of transverse collecting ducts and helps in the passing of the sperms. So, the correct answer is option B.